Opengl/Glut 键盘输入问题

Posted 2023-02-16

【中文标题】Opengl/Glut 键盘输入问题

【英文标题】：Opengl/Glut keyboard input trouble

【发布时间】：2020-02-19 15:58:38

【问题描述】：

我有一个任务是在屏幕上绘制一个金字塔，然后在我按下键盘上的“k”键后旋转。 一切正常，除了旋转部分，因为程序似乎没有注意到我按下键。代码如下：

void changeSize(int w, int h) 

    if(h == 0)
        h = 1;

    float ratio = w * 1.0 / h;

    glMatrixMode(GL_PROJECTION);
    glLoadIdentity();

    glViewport(0, 0, w, h);

    // Set perspective
    gluPerspective(45.0f ,ratio, 1.0f ,1000.0f);

    // return to the model view matrix mode
    glMatrixMode(GL_MODELVIEW);


void renderScene(void) 

    // clear buffers
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

    // set the camera
    glLoadIdentity();
    gluLookAt(5.0,5.0,5.0,
              0.0,0.0,0.0,
              0.0f,2.0f,0.0f);

    // put the geometric transformations here

    // put drawing instructions here

    glPolygonMode(GL_FRONT_AND_BACK,GL_LINE);

    glBegin(GL_LINES);
        glColor3f(1.0f, 0.0f, 0.0f);
        glVertex3f(-100.0f, 0.0f, 0.0f);
        glVertex3f( 100.0f, 0.0f, 0.0f);

        glColor3f(0.0f, 1.0f, 0.0f);
        glVertex3f(0.0f, -100.0f, 0.0f);
        glVertex3f(0.0f, 100.0f, 0.0f);

        glColor3f(0.0f, 0.0f, 1.0f);
        glVertex3f(0.0f, 0.0f, -100.0f);
        glVertex3f(0.0f, 0.0f, 100.0f);
    glEnd();

    //triangulos da base
    glBegin(GL_TRIANGLES);
        glColor3f(255.0f,255.0f,255.0f);
        glVertex3f(1.0f,0.0f,1.0f);
        glVertex3f(-1.0f,0.0f,-1.0f);
        glVertex3f(-1.0f,0.0f,1.0f);
    glEnd();

    glBegin(GL_TRIANGLES);
        glVertex3f(1.0f,0.0f,1.0f);
        glVertex3f(1.0f,0.0f,-1.0f);
        glVertex3f(-1.0f,0.0f,-1.0f);
    glEnd();

    //triangulos das faces

    glBegin(GL_TRIANGLES);
        glVertex3f(1.0f,0.0f,1.0f);
        glVertex3f(0.0f,2.0f,0.0f);
        glVertex3f(-1.0f,0.0f,1.0f);
    glEnd();

    glBegin(GL_TRIANGLES);
        glVertex3f(1.0f,0.0f,-1.0f);
        glVertex3f(0.0f,2.0f,0.0f);
        glVertex3f(1.0f,0.0f,1.0f);
    glEnd();

    glBegin(GL_TRIANGLES);
        glVertex3f(1.0f,0.0f,-1.0f);
        glVertex3f(0.0f,2.0f,0.0f);
        glVertex3f(-1.0f,0.0f,-1.0f);
    glEnd();

    glBegin(GL_TRIANGLES);
        glVertex3f(-1.0f,0.0f,-1.0f);
        glVertex3f(0.0f,2.0f,0.0f);
        glVertex3f(-1.0f,0.0f,1.0f);
    glEnd();

    // End of frame
    glutSwapBuffers();


// write function to process keyboard events

void rotate (unsigned char key, int x, int y) 
    if (key == 'k') 
        glRotatef(45,1.0,1.0,0.0);

        glutPostRedisplay();


int main(int argc, char **argv) 

    // init GLUT and the window
    glutInit(&argc, argv);
    glutInitDisplayMode(GLUT_DEPTH|GLUT_DOUBLE|GLUT_RGBA);
    glutInitWindowPosition(100,100);
    glutInitWindowSize(1200,1200);
    glutCreateWindow("CG@DI-UM");

    // Required callback registry 
        glutDisplayFunc(renderScene);
        glutReshapeFunc(changeSize);


    // put here the registration of the keyboard callbacks
        glutKeyboardFunc(rotate);

    //  OpenGL settings
    glEnable(GL_DEPTH_TEST);
    glEnable(GL_CULL_FACE);

    // enter GLUT's main cycle
    glutMainLoop();

    return 0;

我的程序似乎没有注意到我在按下键。我尝试只打印正在按下的键，这很有效，所以我真的迷路了。

【问题讨论】：

问题解决了吗？请告诉我缺少什么。请阅读What should I do when someone answers my question?

【参考方案1】：

glRotatef 在rotate 中似乎没有作用，因为glLoadIdentity() 在renderScene 的开头被调用。实际上glRotatef 改变了当前矩阵，但是当场景被渲染时（renderScene），然后glLoadIdentity() 将Identity matrix 加载到当前矩阵。 无论如何，在输入事件回调中对当前矩阵进行更改是一种不好的风格。在renderScene 中渲染场景之前，更改输入事件中变量的状态和值，并使用变量设置当前模型视图矩阵。

添加一个全局变量angle：

float angle = 0.0f;

更改renderScene 中变量的值。例如：

void rotate (unsigned char key, int x, int y) 
    if (key == 'k') 
        angle += 45.0f;
        glutPostRedisplay();
    

并将旋转应用于renderScene中的当前矩阵：

void renderScene(void) 

    // clear buffers
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

    // set the camera
    glLoadIdentity();
    gluLookAt(5.0,5.0,5.0,
              0.0,0.0,0.0,
              0.0f,2.0f,0.0f);

    // apply rotation
    glRotatef(angle, 1.0f, 1.0f, 0.0f);

    // [...]